124 THE IDEAL TYPES OF THE 



all of which are united by nervous threads (c) into a ring, which 

 is often called the nervous collar. 



In Mollusca, (figs. 59, 60,) there is, as before, a distinct intestine 

 (m, ma, a) in the centre, but the heart (h), as a general thing, 

 is more concentrated than that of the Zoophyta, and the ner- 

 vous system (en, g, g 1 , g 2 , c, ga, no, nc 1 , nc 2 ) preponderates on the 

 side opposite to the heart (h), whilst there is one or more gangli- 

 ons (g) next to it. All of these ganglions are united by, nervous 

 threads (c) into an irregular circle about the body. The Mollusca 

 were considered by Cuvier as next in rank to the highest animals, 

 the Vertebrata; and such is the opinion of the most eminent of 

 all his successors, Richard Owen. The reason is obvious ; for 

 the Mollusca, especially that group of them which comprises the 

 Cuttle-fishes and Argonautas and Nautilus, have an organization 

 which in part is more nearly related, in complicity and kind, to 

 the Vertebrates, than is that of any of the other grand divisions. 

 I have said that the Molluscan organization is, in part, superior 

 to that of all others below Vertebrates ; for anatomical investi- 

 gations of later years, and observations upon the intelligence 

 of Insects, have led many naturalists to look upon Articulata as 

 parallel with Mollusca in point of rank. Let us see what is the 

 tendency among them as regards the nervous system, the ruling 

 power of life. 



In Articulata, (figs. 61, 62,) the intestine, (m,ma,a,) still in the 

 centre, is bordered on one side by the heart, (A,) as in previous 

 groups, and on the opposite side we find the nervous system, 

 (en, g, c, nc, nc 1 ,) nearly altogether concentrated along a median 

 line, and showing a strong advance toward the head, but on 

 the side next the heart (h) a single ganglion (g) which is united 

 to the main group by a nervous ring (c). The tendency to con- 

 centrate the life-giving system toward the head is illustrated by 

 the longitudinal section. 



In the Vertebrata, (figs. 63, 64,) we have the highest degree 

 of concentration of the nervous system, (en, g, c, c 1 , nc, we 1 ). 

 The main group of nerves is massed as a single chain, (en, nc,) 

 still with traces of a double character, as in Articulata, and 



